Measurement and control of output or transmit power in radio frequency (RF) wireless transmission systems has always been important, for example to ensure that the power of the transmitted signal meets regulatory requirements, to ensure that components such as a power amplifier in the transmit chain are operating within safe limits, and to minimise current consumption in the transmit chain, and therefore minimise power consumption.
One widely used method for measuring and tracking output or transmit power in wireless transmitters involves measuring a peak output voltage and using the measured peak output voltage to estimate the output or transmit power. However, this method is prone to significant error when the output impedance of the transmitter differs from a default value. As a result a power control system of the transmitter could be misled, and the performance, for example the linearity, current consumption or transmit power mask, of the transmitter could deteriorate significantly.
Accordingly, a more accurate and reliable method for measuring output transmit power is required.